The present invention relates to a multiplex transmission system, and more particularly to a multiplex transmission system which is well suited for application within a control panel and a control device, between a plurality of control panels, or between a control panel and a control device.
Heretofore, such controllers as switches and levers and such indicators as lamps and meters within a control panel are connected to a plurality of control devices through cables. In recent years, the promotion of automation and the intensification of monitoring functions in a plant have increased the number of cables, so that wiring operations have become conspicuously troublesome and the period of time necessary for the wiring has been prolonged.
For the simplification of the wiring operations, the adoption of multiplex transmission technology is readily considered particularly when digital signals are to be handled.
Cables which are connected to the controllers and indicators within the control panel are first collected by a multiplex transmission processing unit. Also in the plurality of control devices, the cables of signals to be coupled with the control panel are collected by respective multiplex transmission processing units. With this measure, the cables between the control panel and each control device are collected into a single cable, and a sharp reduction in the number of cables becomes possible.
With the multiplex transmission technology, however, attention must be paid to the directivities of signals ordinarily. Regarding the controller and the indicator, the transmission directions of their respective signals are opposite within the control panel. As to the former, the signal is transmitted toward the control device, whereas as to the latter, the signal is transmitted so as to arrive from the control device. In connecting the cables to the multiplex transmission processing units, accordingly, consideration must be given to such directivities of the signals.
The prior-art multiplex transmission system as described above includes a multiplex transmission processing unit TRU(1) in the control panel, and the multiplex transmission processing unit TRU(2) in the control device. The multiplex transmission processing unit TRU(1) has a transmitter T.sub.1 and a receiver R.sub.1, and also has a serializer or parallel-to-series converter P/S.sub.1 connected to the transmitter T.sub.1 and a deserializer or series-to-parallel converter S/P.sub.1 connected to the receiver R.sub.1. The multiplex transmission processing unit TRU(2) has a transmitter T.sub.2 and a receiver R.sub.2, and also has a serializer P/S.sub.2 connected to the transmitter T.sub.2 and a deserializer S/P.sub.2 connected to the receiver R.sub.2. The transmitter T.sub.1 and the receiver R.sub.2 are connected by a cable CA.sub.1. A cable CA.sub.2 connects the transmitter T.sub.2 and the receiver R.sub.1. Among the cables within the control panel, those for transmitting the signals toward the control device are fixed to the serializer P/S.sub.1. The remaining cables within the control panel for receiving the signals sent from the control device are fixed to the deserializer S/P.sub.1. Likewise to those within the control panel, the respective cables are fixed to the serializer P/S.sub.2 and deserializer S/P.sub.2 of the multiplex transmisstion processing unit TRU(2) within the control device.
At the time of design and in the wiring operations, accordingly, which of the terminals of the serializer P/S and the deserializer S/P the cables C must be connected to need to be determined depending upon the transmission directions of the signals of the respective cables C as stated before. In general, the numbers of terminals of the serializer P/S and the deserializer S/P are predetermined. For this reason, as the cables C are connected to the terminals of the serializer P/S and the deserializer S/P, it can occur that more of the terminals of the serializer P/S are provided than needed, whereas the number of terminals of the deserializer S/P are is insufficient. That is, wiring alterations and additional wiring which sometimes take place during the adjustments of the plant cannot be flexibly coped with.